The metabolism of pteroylglutamic acid by the rat

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Abstract
Young rats when injected with pteroylglutamic acid (PGA) increase the urinary excretion of folic acid (FA) and citrovorum factor (CF), but the recovery decreases with increasing doses. At each excretion level, CF accounts for only 0.5-3% of the total FA. In liver more CF than unconverted FA is found. Whereas administration of 0.05-2.0 mg of PGA/100 g body weight increases the CF content of the liver by only a few micrograms without increasing the concentration of unconverted FA, larger doses (5-20 mg/100 g) lead to a higher storage of unconverted FA without further increases in the CF level. As a consequence, the ratio of CF to unconverted FA is decreased. Ascorbic acid, when injected together with PGA, increases the urinary excretion of both FA and CF. It raises the liver level of CF and, when injected in larger doses, leads to an increased storage of unconverted FA as well. Under these conditions the ratio of CF to unconverted FA is again diminished. Rats treated with phenobarbital increase their excretion of both ascorbic acid and CF. In vitro addition of ascorbic acid to collected urine is without any influence on its CF concentrations. Low-protein and protein-free diets lower the liver content of CF and the ratio of CF to unconverted FA. In severe protein deficiency the ability of the liver to store injected PGA is also impaired. It is concluded that lack of dietary protein depresses the capacity of the liver to convert PGA into CF. Both high-fat diets and fat accumulation in the liver due to choline deficiency do not impair its capacity to form CF.